1. Technical Field
The present invention relates to an optical encoder having an optical encoding disc.
2. Description of Related Art
Optical encoders use optical signal to detect mechanical positions and motions in various types of systems. The mechanical positions and motions detected by optical encoders can be related to linear or rotational displacements of moveable components, such as shafts of motors.
A conventional optical encoder typically includes a light source module, an optical encoding disc, and a plurality of photo-detectors. The optical encoding disc made of a glass substrate includes a plurality of concentric annular tracks. Each track has a different pattern so that the optical encoding disc has a different combination of patterns with respect to different angular positions of the optical encoding disc.
The pattern of each track is generally constituted by a plurality of light pervious portions and a plurality of light blocking portions. The light blocking portions are formed by coating a light blocking film on the glass substrate. Portions of the glass substrate free of the light blocking film function as the light pervious portions. However, it is relatively expensive to make the optical encoding disc by film coating. Accordingly, the cost of the optical encoding disc and the optical encoder is relatively high.
Therefore, a new optical encoding disc and a new encoder having the same are desired to overcome the above mentioned problems.